Step-by-step explanation:
Acid-base titration is performed when we want to find out the concentration (usually the concentration in amount of matter (in mol/L).
The statement explains that a titration was carried out in which the titrated (solution whose concentration is unknown) is HCl (hydrochloric acid - acid). The titrant (solution placed in the burette to react with HCl) was KOH (sodium hydroxide – a base). With this titration, the following data were obtained:
MKOH = 0.500 M
VKOH = 45.0 mL
VHCl = 25.0 mL
MHCl = ??
To solve this exercise and find the concentration in mol/L of HCl, the first step is to know how to write the equation that represents the neutralization reaction that occurred and balance it correctly. Neutralization reactions follow the following scheme: acid + base → salt + water.
In this case, the following reaction occurred: KOH + HCl → KCl + H2O
Note that the equation is already balanced. Balancing the equation correctly is important because we need to look at the stoichiometric ratio between the reactants, which in this case is 1 : 1.
The second step is to relate the obtained data. Since a total neutralization reaction took place, this means that the number of H+ ions and OH- ions present in the medium became equal. So we have:
nHCl = nKOH
Knowing that n = M . V, we can perform the following substitution:
nHCl = nKOH
MHCl. VHCl = MKOH. VKOH
You can use this formula (M1 . V1 = M2 . V2) to solve all titration cases. However, remember to put the stoichiometric ratio. In this case, the ratio is 1 : 1 , so it doesn't affect the formula. But if the ratio were, for example, 2 : 1, we would have to use the formula as follows: 2. M1 . V1 = M2. V2. Let's proceed with the calculations:
MHCl. VHCl = MKOH. VKOH
MHCl x 25 = 0.5 x 45
MHCl = 22.5/25
MHCl = 0.9 mol/L
Note that it was not necessary to change the volume units from mL to L because they cancel out in the formula.
Answer: MHCl = 0.9 mol/L